In a gas turbine for power generation including a compressor, a combustor, and a turbine, the output of the turbine is affected by the temperature of intake air suctioned into the compressor. For instance, in summer, when the ambient temperature is high, the density of the intake air decreases and the mass flow rate decreases, which results in a decrease in the output of the turbine. To prevent such a decrease in the output of the turbine, conventionally used is an intake-air cooling device which sprays coolant water to the intake air having a high temperature and cools the intake air by utilizing the evaporative latent heat of the water.
When intake air is cooled by an intake-air cooling device, if the relative humidity exceeds 100% due to over-fogging, the excessively sprayed mist turns into drain water. If such drain water enters a compressor at a wake flow side, there is a risk that the compressor gets locked, for instance, and gets out of order. Thus, it is necessary to adjust the amount of cooling medium, which is to be sprayed to the intake air, in accordance with atmospheric conditions such as a temperature and a humidity so as to prevent over-fogging when the intake air is cooled with the intake-air cooling device. Patent Literature 1 discloses an intake-air cooling device which includes a plurality of cooling-medium supply systems to adjust the amount of cooling medium which is to be sprayed to intake air and vaporizes a cooling medium efficiently so as to prevent over-fogging by switching each cooling-medium supply system between on and off in accordance with the atmospheric conditions.